The quality of residuum feeds, particularly bitumen (heavy oil), suffers from high levels of heteroatoms (nitrogen, oxygen and sulfur) and metals (nickel, vanadium and iron). Refining and/or conversion of such sulfur-laden crudes is costly due to the hydrogen needed to remove the sulfur. As environmental pressures continue to lower allowable emission levels in mogas and diesel products, refining costs continue to rise.
Penalty costs for sulfur-laden feeds in refineries can be exorbitant. Hence, desulfurization of such feeds has become a critical target. Thus, there is a need for low-cost processes which upgrade oils to more environmentally friendly and more profitable feedstocks.
Much work has been done utilizing molten caustic to desulfurize coals. For example, see "Molten Hydroxide Coal Desulfurization Using Model Systems," Utz, Friedman and Soboczenski, 51-17 (Fossil Fuels, Derivatives, and Related Products, ACS Symp. Serv., 319 (Fossil Fuels Util.), 51-62, 1986 CA 105 (24):211446Z); "An Overview of the Chemistry of the Molten-caustic Leaching Process," Gala, Hemant, Srivastava, Rhee, Kee, Hucko, and Richard, 51-6 (Fossil Fuels, Derivatives and Related Products), Coal Prep. (Gordon & Breach), 71-1-2, 1-28, 1989 CA112(2):9527r; and Base-catalyzed Desulfurization and Heteroatom Elimination from Coal-model Heteroaromatic Compounds," 51-17 (Fossil Fuels, Derivatives, and Related Products, Coal Sci. Technol., 11 (Int. Conf. Coal Sci., 1987), 435-8, CA 108(18):153295y).
Additionally, work has been done utilizing aqueous caustic to desulfurize carbonaceous material. U.S. Pat. No. 4,437,980 discusses desulfurizing, deasphalting and demetallating carbonaceous material in the presence of molten potassium hydroxide, hydrogen and water at temperatures of about 350.degree. to about 550.degree. C. U.S. Pat. No. 4,566,965 discloses a method for removal of nitrogen and sulfur from oil shale with a basic solution comprised of one or more hydroxides of the alkali metals and alkaline earth metals at temperatures ranging from about 50.degree. to about 350.degree. C.
Methods also exist for the regeneration of aqueous alkali metal. See e.g., U.S. Pat. No. 4,163,043 discussing regeneration of aqueous solutions of Na, K and/or ammonium sulfide by contact with Cu oxide powder yielding precipitated sulfide which is separated and re-oxidized to copper oxide at elevated temperatures and an aqueous solution enriched in NaOH, KOH or NH.sub.3. Romanian patent RO-101296-A describes residual sodium sulfide removal wherein the sulfides are recovered by washing first with mineral acids (e.g., hydrochloric acid or sulfuric acid) and then with sodium hydroxide or carbonate to form sodium sulfide followed by a final purification comprising using iron turnings to give insoluble ferrous sulfide.
What is needed in the art is a continuous in-situ process for removal of organic sulfur, bound as sulfides, mercaptans and/or thiophenes, which further allows for recovery and regeneration of the desulfurizing agent.